E 1195 – 01 Designation E 1195 – 01 Standard Test Method for Determining a Sorption Constant ( Koc) for an Organic Chemical in Soil and Sediments 1 This standard is issued under the fixed designation[.]
Designation: E 1195 – 01 Standard Test Method for Determining a Sorption Constant (Koc) for an Organic Chemical in Soil and Sediments1 This standard is issued under the fixed designation E 1195; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision A number in parentheses indicates the year of last reapproval A superscript epsilon (e) indicates an editorial change since the last revision or reapproval Scope 1.1 This test method describes a procedure for determining the partitioning of organic chemicals between water and soil or sediment The goal is to obtain a single value which can be used to predict partitioning under a variety of environmental conditions from the measurement of sorption coefficients for specific solids 1.2 Sorption represents the binding process of chemicals to surfaces of soils or sediments through chemical, or physical, or both interactions 1.3 The sorption of nonpolar organic chemicals, and to some extent polar organic chemicals, is correlated with the organic carbon content of the sorbing solid Charged inorganic and organic molecules may behave differently, and some other property, such as, cation exchange capacity, clay content, or total surface area of sorbing solids, may influence sorption Hydrous metal oxides of iron and aluminum may significantly affect sorption in sediments In order to provide a sorption coefficient that is useful for a wide range of soils and sediments, the coefficient is based on organic carbon content This approach, however, will not apply to all chemicals or all soils and sediments In cases where it does not apply, the investigator may need to seek other methods of relating sorption to the properties of the chemical, soil, or sediment 1.4 It is possible that, in addition to organic carbon, sorption is correlated with the total surface area of sorbing solids This may be particularly important with solids having organic carbon contents so low that sorption to inorganic surfaces is significant in comparison to sorption by organic material In such a case, inclusion of the total surface area into the sorption calculation may be useful For further information on this subject see Ref (1).2 1.5 Equilibrium sorption coefficients are determined It is recognized that equilibrium conditions not always exist in environmental situations, but sorption equilibria values are necessary for making generalizations about environmental partitioning 1.6 Studies are conducted preferably with an analytical or technical-grade chemical Mixtures are used only if analytical methods allow measurement of individual components of interest in the mixture Good laboratory procedures must be followed to ensure validity of the data 1.7 This standard does not purport to address all of the safety problems, if any, associated with its use It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use Referenced Documents 2.1 ASTM Standards: D 421 Practice for Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil Constants3 D 422 Test Method for Particle-Size Analysis of Soils3 D 1193 Specification for Reagent Water4 D 4129 Test Method for Total and Organic Carbon in Water by Oxidation Coulometric Detection5 2.2 Other standards: OECD Test Guideline 1066 Terminology Definitions 3.1 sorption distribution coeffıcient (Kd)—the concentration of chemical sorbed by solids, in µg/g, on an oven-dry solids weight basis divided by the concentration of chemical in the water, in µg/g, at equilibrium This test method is under the jurisdiction of ASTM Committee E47 on Biological Effects and Environmental Fate and is the direct responsibility of Subcommittee E47.04 on Environmental Fate of Chemical Substances Current edition approved Oct 10, 2001 Published November 2001 Originally published as E 1195-87 Last previous edition E 1195-87 (Reapproved 1993)e1 The boldface numbers in parentheses refer to the list of references at the end of this test method Annual Book of ASTM Standards, Vol 04.08 Annual Book of ASTM Standards, Vol 11.01 Annual Book of ASTM Standards, Vol 11.02 Available from the Organization for Economic Co-Operation and Delevopment 2, rue André Pascal F-75775 Paris Cedex 16 France Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States E 1195 – 01 sorbed concentrations not exceed typical environmental loading Errors arising from concentration effects at low environmental concentrations usually are less than the variation existing between different solids, when dealing with sorption trends in a general manner Therefore, the initial concentration of the test chemical in solution should not exceed 0.5 of its water solubility 5.5 As an option, a procedure is given for determining concentration effects on sorption This is because high concentrations may be present in certain environmental situations; such as landfills and spills This procedure should be done at four concentrations over a hundred fold concentration range (for example, 0.1, 0.5, 2, and 10 ppm initial solution concentration) If low solubility presents analytical difficulties, solution concentrations should range over at least one order of magnitude The Freundlich equation is an appropriate expression of these effects: 3.2 organic carbon normalized sorption constant (Koc)—the sorption distribution coefficient, Kd, normalized to the relative organic carbon content (fraction) of the solid oc (Koc = [kd/ %OC] 100) Summary of Test Method 4.1 The sorption coefficient of a chemical is measured by equilibrating an aqueous solution containing an environmentally realistic concentration of the chemical with a known quantity of soil or sediment After reaching equilibrium, the distribution of chemical between the water and the solids is measured by a suitable analytical method If appropriate for the test material, sorption constants are calculated on the basis of the organic carbon content of the solids In addition to reporting single values for each solid, the sorption constants from all solids are averaged and reported as a single value Significance and Use 5.1 Sorption data are useful for evaluating the migratory tendency of chemicals into the air, water, and soil compartments of our environment They can be used in the prediction or estimation of volatility from water and soil, concentration in water, leaching through the soil profile, run-off from land surfaces into natural waters, and biological availability Additional information concerning testing to determine sorption coefficients can be found in OECD test Guide 106 (7) 5.2 This test method assumes that sorption of at least nonpolar organic chemicals is mainly influenced by the organic matter of the soil or sediment solids There is ample evidence in the literature to support this assumption, and the user of this test method should refer to Ref (2) for more information on this subject Organic carbon content is chosen as the basis for sorption instead of organic matter content This is because organic carbon values generally are measured directly by analytical methods Organic matter may be estimated by multiplication of the organic carbon values by a somewhat arbitrary constant of 1.7 (3) This test method is based on the assumption that all of the material sorbed to the solids is reversibly bound The analyses described herein assume equilibrium between the liquid and solid concentrations of the test compound In some cases, there may be a fraction of the compound that is irreversibly bound to the solids For these cases, the measurements made by the test may not reflect a true “equilibrium” The irreversible sorption phenomena has been extensively documented and the reader is referred to (9), (10) and (8) for more discussion on this topic 5.3 A sorption constant is obtained and is essentially independent of soil properties other than organic carbon This value is useful because, once it is determined, the sorption distribution characteristics for any solid can be estimated based on its organic carbon content 5.4 This test method is designed to evaluate sorption at environmentally relevant concentrations as a function of organic carbon content of different soil and sediment solids Therefore, the number of different solids is emphasized in the procedure rather than the number of chemical concentrations studied with each solid In general, one concentration is employed since the test method assumes that at low solution concentrations, sorption isotherms approximate linearity and Ca KCs1/n (1) where: Ca = chemical adsorbed, oven-dry solids weight, µg/g, K = sorption coefficient, Cs = solution concentration at equilibrium, µg/g, and 1/n = exponent 5.5.1 A log plot of the Freundlich equation yields the following linear relationship: log Ca log K 1/n log Cs (2) Apparatus 6.1 High-Speed Temperature Controlled Centrifuge, capable of removing particles 0.1-µm radius from solution Details of centrifugation techniques are given in the Procedure section 6.2 Centrifuge Tubes, capable of withstanding high speed and made of glass, metal, or other suitable material which minimizes adsorption of the test chemical to its surface The tubes should be capped with TFE-fluorocarbon or aluminumlined screw caps 6.3 Analytical Instrumentation, suitable for measuring the concentration of the test chemical in solids and water 6.4 Laboratory Oven, capable of maintaining a temperature of 103 to 110°C The oven is used for determining the moisture content of soils or sediments Reagents and Materials 7.1 Analytical or technical grade chemical of known purity should be used If available, all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society.7 Radiolabeled test materials of known radio-purity or nonlabeled test materials of known composition are suggested 7.2 Purity of Water—Reagent water shall conform to Specification D 1193 for Type IV grade water “Reagent Chemicals, American Chemical Society Specifications,” Am Chemical Soc., Washington, D.C For suggestions on the testing of reagents not listed by the American Chemical Society, see “Reagent Chemicals and Standards,” by Joseph Rosin, D Van Nostrand Co., Inc., New York, NY, and the “United States Pharmacopeia.” E 1195 – 01 Sampling, Test Specimens, and Test Units 8.7 Measure the soil or sediment specimen pH using a 1:1 soil slurry procedure (3) Stir the suspension several times over a 30-min period and allow to stand h Then measure the pH of the supernatant fluid above the soil suspension 8.8 Prepare a test chemical water solution by dissolving the chemical in water Make sure the test concentration is below water solubility and, preferably, near concentrations expected in the environment Unless otherwise indicated, references to water shall be Type IV reagent water Care should be taken with volatile chemicals to minimize losses 8.8.1 For those chemicals with water solubilities in the range of 0.1µ g/g or less, prepare a stock solution using acetonitrile or other appropriate solvent miscible with water Directly add the chemical to the solids and water system with 0.1 % or less volume of the cosolvent If using this method, use the cosolvent at the same concentration in all tests 8.1 Use soils or sediments, or both, varying in organic carbon content, pH, and texture or particle-size distribution Four to seven different samples are recommended Record their history, if available, description, and site location 8.2 Collect soil samples in containers lined with polyethylene bags Collect from the top in of the soil profile and before storing, screen through a 2-mm sieve Store at 4°C Store and handle the soil samples at the moisture content at time of collection If initial moisture content is too high for satisfactory screening, partially dry the soil samples, by exposing to air for brief periods When using air-dried soil samples, longer sorption equilibrium times may be required to allow the organic matter to become thoroughly wetted 8.2.1 Determine the soil pH, particle-size distribution, and organic carbon content for each soil sample Cation or anion exchange capacity may be needed for charged molecules Refer to Ref (3) for measurement methods 8.2.2 Determine the moisture content on a soil specimen allowing sorption to be based on oven-dried solids weight Discard the soil specimen after determining the moisture content 8.3 Sediment samples from aquatic systems should not be air-dried or frozen prior to use Collect sediment samples with a suitable grab or coring device and, if not used immediately, store in a suitable bottle at 4°C for periods up to 10 days Minimal sediment characterization should include organic carbon content and particle-size distribution Work with ions and molecules having functional groups capable of ionizing can be aided by characterization of redox potential, pH, and cation or anion exchange capacity of the sediments 8.3.1 Measurement of sorption properties of anoxic sediments, usually characterized by the presence of a hydrogen sulfide odor, requires strict adherence to oxygen exclusion during a test Admission of even small amounts of oxygen to the diluted sediments suspension will allow oxidation of ferrous iron with a concomitant precipitation of ferric hydroxide, which is a highly efficient scavenger for many dissolved constituents However, when the primary area of concern in the aquatic system is aerobic, conduct the test under a normal air atmosphere using well-aerated sediments For further information consult Ref (4) 8.4 Base the solids content (or conversely, water content) of the soil or sediment specimen on the oven-dry weight (24 h drying at 103 to 110°C) Only in the case of very dilute sediment suspensions (0.1 % solids or less) are dry-weight corrections for dissolved inorganic and organic species required Do not reuse in any sorption measurement the specimens used for this dry-weight solids determination 8.5 Combustion is the preferred measurement method for organic carbon, using the procedures described in Test Method D 4129 or other similar procedures 8.6 Determine the particle-size distribution by a combination of sieving and sedimentation The fractions are gravel (>2 mm), sand (2.0 to 0.05 mm), silt (0.05 to 0.002 mm), and clay (0.1-µm radius and 2.65-g/cm3 density from solution: t5 2.22 1010 ~r/min! ln Rb/Rt (10) where: t = seconds, r/min = revolutions per minute, = distance from center of centrifuge rotor to top of Rt solution in centrifuge tube, cm, and = distance from center of centrifuge rotor to bottom Rb of centrifuge tube, cm 11.2 This assumes spherical particles and: t 9/2 F n v2r2p ~rp r! G ln ~Rb/Rt! (11) where: v2 = 4p2 ~r/min! 3600 , rp = particle radius = 10−5 cm, n = viscosity of water at 25°C = 8.95 10−3 g/s cm, rp = particle density = 2.65 g/cm3, and r = density of water = 1.0 g/cm3 In general practice double the calculated times to ensure complete separation 11.3 Moisture percentage of solids: M5 ~A B! 100 B (12) where: M = moisture percentage, A = sample wet weight, g, and B = sample oven-dry weight, g 11.4 Oven-dry solids weight in wet solids sample: A B 1 M/100 (13) where: B = oven-dry solids weight, g, A = sample wet weight, g, and M = moisture percentage 11.5 Total water present: FIG Relationship Between Water to Soil Ratios and Kd at Various Percentages of Sorbed Material WT W A ~ A B ! (14) E 1195 – 01 Cs where: WT = total quantity of water, mL, WA = volume of water added, mL, A = wet weight of solids, g, and B = oven-dry weight of solids, g 11.6 Total chemical in water: T ~ W T ! ~ CS ! = concentration of chemical in solution at equilibrium, µg/mL, and 1/n = exponent A plot of log Ca versus log Cs is constructed where: 1n slope and log K intercept 11.10 Calculation of organic carbon normalized sorption constant (Koc): (15) Kd 100 Koc % OC where: T = total quantity of chemical left in water, µg, WT = total quantity of water, mL, and Cs = concentration of chemical in water, µg/mL 11.7 Total chemical in solids (no breakdown): GS GA T (16) 12 Precision and Bias 12.1 An interlaboratory test program of this test method was conducted at four laboratories using trifluralin and 13 soil types Each laboratory used two to four soil types, differing in each laboratory The percent organic carbon of each soil type, sorption coefficient, and organic carbon normalized sorption constant are given in Table If one soil (No 8) is excluded from the mean, the correction of sorption data for organic carbon content reduces the variability from 69 to 38 % in this particular study In general, one can probably anticipate variations of 20 to 50 % of the mean Kocvalue This may seem like a large variation, but it is actually small with respect to the range of Koc values covered by chemicals This range is from zero to more than 105 (17) where: Kd = GS = B = Cs = sorption coefficient, total quantity of chemical sorbed to solids, µg, oven-dry weight of solids, g, and concentration of chemical in water at sorption equilibrium, µg/mL 11.9 Calculation of sorption coefficient (K) and 1/n using Freundlich equation for concentration study: log Ca log K 1/n log Cs (20) where: = organic carbon normalized sorption constant, Koc = sorption distribution coefficient, and Kd % OC = percentage of organic carbon in solids 11.11 Then, average the sorption constants for the different soil samples to determine a mean Koc value, the standard deviation, and the coefficient of variation where: GS = total quantity of chemical sorbed to solids, µg, GA = total quantity of chemical in control sample, µg, and T = total quantity of chemical left in water, µg 11.8 Calculation of sorption coefficient (Kd): GS/B Kd C s (19) (18) where: K = sorption coefficient, Ca = concentration of chemical in solids at equilibrium, µg/g (Gs/B), 13 Keywords 13.1 equilibrium sorption coefficients; partitioning of organic chemicals; sorption constant (Koc) E 1195 – 01 TABLE Sorption of Trifluralin by Thirteen Soils from Interlaboratory Study Soil Organic Carbon,% 10 11 12 13 0.41 0.52 0.70 0.73 0.77 1.07 1.40 1.80 1.84 1.96 2.00 2.60 3.37 Mean SD Coefficient Variation Excluding Soil No Mean SD Coefficient Variation Kd Koc 15.5 37.7 17.0 35.6 19.5 66.7 130.0 270.0 139.0 155.0 130.0 150.0 158.0 101.8 76.7 75.3 % 750 250 400 870 540 230 300 14 990 590 900 500 770 710 450 300 51.1 % 87.8 60.4 % 68.7 % 730 150 37.6 % APPENDIXES (Nonmandatory Information) X1 Ranking Sorption Tendencies X1.1 The Koc value of a chemical obtained from this test method represents a single value which characterizes the partitioning of a chemical between soils or sediments and water This value then can be used in the evaluation of the fate and behavior of the chemical in the environment It represents a parameter which is essentially independent of soil properties, such that a basis is established for ranking and comparing chemicals with respect to their soil to water partitioning tendencies An example of such a ranking is given in Table X1.1 TABLE X1.1 Sorption Constants for Several Chemicals Koc Chemical Dicamba Cis 1,3-dichloropropene Ethylene dibromide Monuron DBCP Atrazine EPTO Nitrapyrin Lindane Trifluralin Parathion Chlorpyrifos DDT 26 32 83 130 170 280 460 735 300 800 100 150 000 E 1195 – 01 X2 Soil Mobility Chemicals which have a low Koc value are weakly sorbed and are therefore more mobile in soil A mobility classification scheme based on Koc values is given in the Table X2.1 X2.1 This process enables one to classify particular aspects of chemical behavior regarding various environmental transport processes For example, the Koc value represents an expression of the inherent mobility of chemicals in soil TABLE X2.1 Recommended Classification of Soil Mobility Potential of Chemicals Koc 0–50 50–150 150–500 500–2000 2000–5000 5000 Mobility Class very high high medium low slight immobile X3 Sorption Effects on Volatilization X3.1 Volatility of chemicals from soils or aquatic systems is modified by the sorption characteristics of the compound If two chemicals have the same tendency to volatilize from a simple water environment, the one which is sorbed the least will demonstrate the highest potential for volatility transport in an environmental situation where soil or sediment is also present (for example a pond or a field) This is simply a result of the sorption process modifying the concentration of the chemical in the aqueous phase and in turn modifying the volatility characteristics of the compound (6) X4 Mathematical Models for Chemical Fate Estimates be obtained from the Koc value and used in the modeling process Therefore, this type of measurement can be extremely useful in evaluating expected distribution patterns of chemicals in the environment X4.1 In addition, the Koc value is easily utilized in environmental modeling systems which combine all the environmental parameters that effect the fate of chemicals in the environment For differing amounts of organic carbon selected to represent model systems, fairly reliable estimates of Kd can REFERENCES (1) Pionke, H B., and Deangelis, R J.,“ Method for Distributing Pesticide Loss in Field Run-off Between the Solution and Absorbed Phase,” CREAMS, A Field Scale Model for Chemicals, Run-off and Erosion from Agricultural Management Systems, Chapter 19, Vol III: Supporting Documentation, USDA Conservation Research Report, 1980 (2) Goring, C A I., and Hamaker, J W., eds, Organic Chemicals in the Soil Environment, Vol I, Marcel Dekker, Inc., New York, NY, 1972, pp 49–143 (3) Black, C A., Evans, D D., White, J L., Ensminger, L E., and Clark, F E., eds, Methods of Soil Analysis, Vol and 2, American Society of Agronomy, Madison, WI, 1965 (4) Jones, R A., and Lee, G F., “Evaluation of the Elutriate Test as a Method of Predicting Contaminant Release During Open Water Disposal of Dredged Sediment and Environmental Impact of Open Water Dredged Material Disposal,” Vol I: Discussion, Technical Report D78-45, U.S Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, August 1978 (5) Hance, R J., “The Speed of Attainment of Sorption Equilibria in Some Systems Involving Herbicides,” Weed Research, Vol 7, 1967, pp 29–36 (6) Laskowski, D A., Goring, C A I., McCall, P J., and Swann, R L., Terrestrial Environment in Environmental Risk Analysis for Chemicals, Van Nostrand Reinhold Company, New York, NY, 1980 (7) OECD Test Guideline 106 (8) Fu, G., A Kan, and M Tomson “Adsorption and Desorption Hysteresis for PAHs in Surface Sediment.” Environmental Toxicology and Chemistry,13:10, 1559–1567, 1994 (9) Kan, A.T., G Fu, W Chen, C.H Ward, and M.B Tomson “Irreversible Adsorption of Neutral Organic Hydrocarbons: Experimental Observations and Model Predictions.”Environmental Science and Technology, 32:3 892–902, 1998 (10) Kan, A., G Fu, and M Tomson “Adsorption/Desortion Hysteresis in Organic Pollutant and Soil/Sediment Interaction”, Environmental Science and Technology, 28, 859–867, 1994 E 1195 – 01 ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility This standard is subject to revision at any time by the 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